The present invention relates to an image forming apparatus, and more specifically, to an image forming apparatus in which a plurality of development cartridges containing the same color toners are mounted, and capable of reducing bad effects as much as possible, the bad effects being occurred by operating a development cartridge to be operated excluding and not operating the remaining development cartridges.
Also, the present invention relates to an image forming apparatus, and more specifically, to an image forming apparatus which can smoothly continue an image forming operation when a plurality of development cartridges containing the same color toners are mounted to form a monochromatic image.
Conventionally, an image forming apparatus, using an electro-photographic recording method, in which an electrostatic latent image is exposed and formed on the surface of a carrier made of a photoreceptor is known. In the image forming apparatus, a toner image on the surface of the carrier, which is carried by developing the electrostatic latent image with toner, is transferred to a recording medium such as a recording sheet to thereby form an image. The electrostatic latent image is developed with toner by rotating a developing roller facing the surface of the carrier, and transferring and sticking toner on the surface of the developing roller to the carrier. The developing roller is supplied with toner by rotating a supply roller rotating within a toner containing space in pressure contact with the developing roller.
In the image forming apparatus employing such an electro-photographic recording method, a development cartridge in which a developing roller and a supply roller are arranged in a container containing toner is attached or removed to replenish toner. As the image forming apparatus, an image forming apparatus having a construction in which a plurality of development cartridges is mountably configured, and the same color toners are contained within the development cartridges has been suggested. In this case, a development cartridge which sticks toner to the surface of the carrier is changed over at a timing of runout of toner, so that the number of replenishment of toner can be reduced to continue image forming (for example, see JP-A-2002-351190 and JP-A-2003-316106).
The image forming apparatuses disclosed in JP-A-2002-351190 and JP-A-2003-316106, are rotary type image forming apparatuses in which a plurality of development cartridges are accommodated and mounted around a rotating shaft of a rotary unit. However, there is also a tandem type image forming apparatus in which a plurality of development cartridges or carries is juxtaposed linearly.
As thus described, in the image forming apparatuses to which a plurality of development cartridges can be mounted, as disclosed in JP-A-2002-351190 and JP-A-2003-316106, a development cartridge facing the carrier is changed over to the next development cartridge after runout of toner in the facing development cartridge, thereby image forming does not need a work of replenishing toner. In addition, JP-A-2002-351190 discloses a changing over of a development cartridges before a toner around the supply roller runs out. This construction permits eliminating the timing for determining whether or not toner runs out completely and development becomes disabled, and realizing more continuous image forming.
Further, as such image forming apparatuses, an image forming apparatus in which only a developing roller and a supply roller of a development cartridge which faces the surface of a carrier and develops an electrostatic latent image is coupled with a driving source to transmit a rotational driving force is known.
However, in this type of image forming apparatus, since the remaining development cartridges excluding a development cartridge which performs image forming processing remains stationary, a state in which the developing roller and the supply roller are pressure-contacted with each other at the same place lasts. Therefore, when a development cartridge is changed over to perform new image forming, the effects may appear. Specifically, when a developing roller stops for a prolonged period of time, a trace which has been pressure-contacted with a supply roller may remain on the surface of the developing roller. In this case, when toner is stuck onto the surface of the carrier, a place corresponding to the position of pressure contact and other places does not match. As a result, for a while after starting to form an image, a striped trace (so called, leaving banding) for every one rotation of the developing roller may appear in a toner image, which may deteriorate the quality of an image to be formed.
Although a case in which a trace of pressure contact with the supply roller appears in a toner image as so-called leaving banding during a period for which the developing roller stops which deteriorates the image quality is described as an example in the present specification, the present invention is not limited thereto. A case in which a difference in characteristics may occur during the stopping period of development cartridges is also included because the developing surface of the developing roller is divided into two of inside and outside. If exposure period to the outside becomes, for example, long, a toner to stick to changes in quality, and it is included in a problem by leaving banding when development surface of a developing roller changes in quality by a toner to stick to. In addition, such problems are solved by rotating the developing roller.
Moreover, an another image forming apparatus suggests a construction which permits an image forming operation without causing a problem, such as noise, even when development cartridges are not accommodated (mounted) at all accommodating positions of the rotary unit (for example, see JP-A-2003-50494).
However, in a case in which development cartridges containing the same color toners are not mounted at accommodating positions adjacent to the developing rotary unit, when a toner within a development cartridge used runs out in forming a large amount of monochromatic images, the rotational operation (the changeover operation of development cartridges) should be repeated to move a development cartridge to be used to a developing position, which may take much time.
Here, as the image forming apparatus including the rotary unit, an image forming apparatus provided with a partition plate which partitions the interior of a container of a development cartridge, which contains toner, into a small space within which a supply roller rotates is known. In the image forming apparatus, it is necessary to put together (refresh) the toner within the container once by rotating the rotary unit so as to turn a development cartridge upside down after a certain amount of images has been formed, and then perform an action of replenishing toner into the space within which the supply roller rotates.
Specifically, in such as image forming apparatus, even before the toner within the development cartridge runs out, an action of replenishing toner into the space within which the supply roller rotates is performed in parallel with performing a changeover operation in which the rotary unit is rotated at a predetermined timing to cause the developing roller to face the carrier.
From the foregoing, even in a case in which the development cartridges containing the same color toners are mounted at all accommodating positions of the rotary unit, if the runout of toner occurs in any one of the development cartridges due to a difference between the consumptions of toner, the rotational operation of the rotary unit should be repeated to move a usable development cartridge to the developing position, similar to the above, even during the rotational operation of the rotary unit accompanied with the operation of replenishing the other development cartridges with toner.
As thus described, when the changeover operation of development cartridges are repeated during continuous image forming operation, an operator suffer from stress because he/she thinks that the image forming is not smoothly performed, which becomes a problem.